Digital video streams typically represent video using a sequence of frames (i.e. still images). An increasing number of applications today make use of digital video stream encoding for purposes other than traditional moving pictures (such as movies and video clips). For example, screen capture and screen casting applications generally represent the output of a computer monitor over time as a digital video stream, irrespective of the specialized nature of the content of the monitor. Typically, screen capture and screen casting digital video streams are encoded using video encoding techniques like those used for traditional moving pictures.
To permit transmission of digital video streams while limiting bandwidth consumption, a number of video compression schemes have been devised, including formats such as VPx, promulgated by Google Inc. of Mountain View, Calif., and H.264, a standard promulgated by ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG), including present and future versions thereof. H.264 is also known as MPEG-4 Part 10 or MPEG-4 AVC (formally, ISO/IEC 14496-10).
These compression schemes may use quantization and transform techniques on the frames of a digital video stream to reduce the bitrate (i.e. encoded data size) of the encoded digital video stream. Such techniques are lossy in nature—meaning that part of the original digital video stream is lost during encoding. Quantization techniques are used to discard part of a frame's data based on standard computations, thereby reducing the frame's bitrate. Quantization is a low-pass technique, which can cause blurring or other effects on a frame.
These effects result in video artifacts around the edges in the frame's contents, such as ring artifacts. These artifacts are especially noticeable in digital video streams containing numerous edges, such as in screen capture and screen casting applications.